The present invention relates to a rotary encoder and, more particularly, to a photoelectric rotary encoder for detecting the rotational speed and the movement distance.
The conventional photoelectric rotary encoder comprises a rotary disc provided with a plurality of slits. The rotary disc is positioned across a light path of a photo-interpreter. The rotation of the disc is detected by detecting the light passing the slits of the disc and outputting signals.
The detection accuracy of the minimum rotational distance depends upon a pitch between the slits of the rotary disc. To increase the accuracy, accordingly the slit pitch must be miniaturized. However, it is very difficult to provide the slits with a fine pitch in the disc. Further, since the slits are provided at the peripheral of the disc in a concentric circle manner, it is impossible to detect the rotation direction of the disc.